Magnetic switching device



April 10, 1951 J. E. BIGELOWV MAGNETIC swrrpnmc DEVICE Filed March 4, 1949 Inventor: John E. Bi W gelow, 5 flun His Attorney.

Patented Apr. 10, 1951 MAGNETIC SWITCHING DEVICE John E. Bigelow, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 4, 1949, Serial No. 79,538

1 Claim. 1

My invention relates to electrical switching devices and more particularly to a new and improved switch of the snap-action type employing the forces of permanent magnets in the actuation thereof.

In electrometer devices normally employed in the measurement of potentials in ion chambers and the like, it is frequently desirable to shortcircuit portions of the electrometers prior to charging the input circuits thereof. It has been found that switching devices employed in the performance of such short-circuiting functions are preferably of the type having the contacts thereof completely electrostatically shielded. It is desirable to provide a positive snap-action to insure switching contact for a certain finite time, and it is likewise desirable to limit the mechanical forces which may be developed within such switch to prevent the development of extraneous piezo-electric or other voltage effects in the insulating members thereof. Furthermore, additional leads to the input circuit of an electrometer device, from an external switch, for example, cannot in general be tolerated, due to increased capacitance of variable nature and the leakage effect of additional insulation.

Accordingly, it is a primary object of my invention to provide a new and improved electrical switching device particularly suitable for use in electrometers and the like.

It is another object of my invention to provide a switching device having completely shielded contacts, a positive snap-action, and an inherent limitation on the internal forces which may be developed therein.

In its broadest aspect, my invention makes use of magnets and the associated forces of attraction and repulsion thereof, to perform switching operations. In particular, in a preferred embodiment described herein, a bridging element comprising a permanent magnet formed of conductive material is arranged to engage one of a pair of conducting members constituting the electrodes of a switch. The bridging element is caused either to engage or disengage the other of the conducting members, thereby forming or breaking an electrical connection therebetween, by manipulation of an actuating element, comprising a second permanent magnet, located in proximity to the first magnet.

For a better understanding of my invention attention is now directed to the following description and to the figures of the accompanying drawing, and also to the appended claim, in

which the features of my invention believed to be novel are set forth.

Fig. 1 is an elevational view, partially in section, of an embodiment of my invention; Figs. 2 and 3 are sectional views of portions of Fig. 1 taken along the lines 22 and 33 respectively; Figs. 4a and 4b are enlarged views of a portion of Fig. 1 showing the switch elements in open and closed relation, respectively; and Fig. 5 is a modification of the arrangement shown in Fig. 4a.

Referring now to Fig. 1, there is shown a switching device applied to an electrometer apparatus of the type frequently used in the measurement of potentials in ion chambers and the like. The switching device shown comprises generally, a group of elements forming a switching mechanism designated by the numeral I, and a second group of elements forming an actuating mechanism designated by the numeral 2. In particular, both groups of elements are assembled on a base plate 3 forming part of the supporting structure of an associated electrometer apparatus.

Actuating mechanism 2 comprises a shaft 4 positioned in a pair of bearings 5 in a pair of supports 6, the latter being attached securely to plate 3. Shaft 4 is free to rotate in bearings 5 and is restrained from longitudinal motion with respect to supports 6 by a pair of collars l attached to shaft 4 and arranged to engage the outer surfaces 8 of supports 6.

An eccentric cam 9 is securely attached to shaft 4 at a point lying between supports 6. A ca m actuating device I0 is arranged to engage cam 9. Cam actuator I0 is represented as having a cylindrical center portion ll, positioned in a cylindrical bore l2 of plate 3, and is arranged to be slidable with respect thereto. Center portion H is provided at one end thereof with a hub portion 13 having a rounded extremity M, the latter being engageable with cam 9. Center portion II is provided at the other end thereof with an enlarged button portion l5 arranged to be actuated manually by an operator. By providing hub l3 and button 15 with transverse dimensions greater than the diameter of bore I2, the longitudinal travel of actuator [0 with respect to plate 3 is limited by interference of hub l3 and button 15 therewith. Actuator I0 is also thereby retained in assembled relation with plate 3.

A torsional spring I6 is arranged to cause a torque to be applied to shaft 4 in a predetermined direction to force cam 9 continuously against cam actuator 10, causing hub I3 to engage plate 3, thereby limiting rotation of shaft 4. One extremity II of torsional spring I6 is anchored securely in one of supports 6, while the other extremity I8 thereof is securely attached to shaft 4 at a point between supports 6.

The function of actuating mechanism I as thus far described is to effect rotation of shaft 4 from an initial position corresponding to the fully released position of actuator I0, to a final position corresponding to a fully depressed position of actuator ID, in response to manipulation of actuator ID by an operator. Fig. 2, representing a sectional view along the lines 2-2 of Fig. 1, shows the manner in which which 9 and shaft 4 are caused to rotate in response to longitudinal motion of actuator I0. Initial positions of actuator I and cam 9, corresponding to the conditions of Fig. 1, are represented by the numerals III and 9 respectively in Fig. 2. A second position of cam 9, represented by the numeral 9',,

corresponding to a second position of actuator l0, represented by the numeral I0, is likewise shown.

Attention is nOW directed to switch mechanism I which comprises, generally, a pair of switching elements or electrodes I9 and 20 electrically insulated from each other by an insulating member 2|, a bridging element 22, and an actuating element 23. In particular electrodes I9 and 23 are represented as portions of an electrometer apparatus, in the operation whereof, under certain conditions, it is desirable to effect a short circuit between electrodes I9 and 20.

Electrode I9 is represented as a generally cylindrical wall having electrode 20, also generally cylindrical and provided with a hub portion 25, positioned concentrically therewithin. Electrodes I9 and 20 are formed of a nonmagnetic conductive material, preferably metal. Insulating member 2I is represented as an annular ring arranged to engage the inner surface of wall I9 and hub 25 of electrode 20. Electrode 20 is provided with a radial bore 24, preferably cylindrical in section, extending partially through electrode 20 from the outer cylindrical surface thereof.

Bridging element 22 is represented as a permanent magnet formed of a highly conductive material. Magnet 22 is preferably of the type generally known as a bar magnet, and is provided at the extremities thereof, with a pair of unlike magnetic poles represented in Fig. l by the letters S and N respectively. Magnet 22 is positioned within bore 24 of electrode 20 and is arranged to be freely slideable therein, and at the same time to be guided thereby to maintain substantial coalignment of magnet 22 and bore 24. The lengths of bore 24 and magnet 22, and the radial clearance between electrodes I9 and 20 are such that a substantial portion of magnet 22 is retained Within bore 24 regardless of the position of magnet 22 therewithin. In particular, when magnet 22 is caused to slide outwardly in bore 24 to make engagement with electrode I9, the guiding and retaining actions described prevent magnet 22 from becoming angularly disposed with respect to bore 24 with possible accompanying binding therewith. In this manner freely sliding action of magnet 22 in bore 24 is assured.

Actuating element 23 is represented as a permanent magnet, preferably of the type having a U-shape, and is provided at the extremities thereof with a pair of unlike magnetic poles represented in Fig. 1 by the letters N and S respectively. Magnet 23 is securely attached to the free extremity of shaft 4 projecting beyond support 6 in the vicinity of electrode I9.

Electrode I9 and the associated elements assembled therewithin are positioned with respect to actuating mechanism 2 in such a manner that polar regions N and S of magnet 23 may alternately be brought into proximity with polar region S of magnet 22, as shaft 4 is caused to rotate by manipulation of cam-actuator I0. Fig. 3 is a partial sectional view along the line 3-3 of Fig. 1 indicating further the relationship of electrodes l9 and 20, magnets 22 and 23, shaft 4, and support 6.

Fig. 4a represents a condition wherein pole N of magnet 23 is positioned in the vicinity of pole S of magnet 22, showing, in particular, how magnetic lines of force 26 between unlike poles N and S of magnets 23 and 22, respectively, interact to cause magnet 22 to have a tendency to be attracted toward magnet 23. Since, as previously mentioned, magnet 22 is freely slidable within bore 24, such forces of attraction cause motion of magnet 22, such motion being arrested when magnet 22 engages the inner surface of electrode I9. Since magnet 22 is electrically conductive and simultaneously engages both electrodes I9 and 20, an electrical connection is formed therebetween, and magnet 22 performs the function of a bridging element between electrodes I9 and 20 as in an electrical switch of conventional type. Under this condition switch mechanism I may be said to be closed.

Fig. 4b represents a condition wherein like magnetic poles are brought into proximity by rotation of magnet 23 through one-half revolution from the position shown in Fig. 4a so that v pole S thereof is positioned in the vicinity of pole S of magnet 22. The magnetic lines of force 21 and 28 between like poles S of magnets 22 and 23 respectively, tend to cause magnet 22 to be repelled from magnet 23. Magnet 22 is thus moved toward the inner extremity of bore 24, such motion being arrested when magnet 22 engages the end wall 29 of bore 24. Under this condition the electrical connection between electrodes I9 and 20 is broken and switch mechanism I may be said to be open.

While the independent modes of operation of switch mechanism I and actuating mechanism 2 have been described, my invention will best be understood by a consideration of the combined operation thereof. Under normal conditions when no external force is applied to button I5, actuator I0 is held by virtue of torsional spring I6 in an extreme outward position. Under this condition like poles S of magnets 22 and 23 are brought into proximity and forces of repulsion therebetween force magnet 22 away from elec trode I9 and cause switch I to be open. If button I5 is depressed by an external force, as, for example, manually by an operator, rotation of shaft 4 and magnet 23 causes unlike poles N of magnet 23 and S of magnet 22 to be brought into proximity. Forces of attraction therebetween cause magnet 22 to engage electrode I9 while simultaneously engaging electrode 20. Under this condition an electrical connection is formed between electrodes I9 and 20 causing switch I to be closed.

While the arrangement described represents, in conventional terminology of the art, a normally-open switch, that is to say,a switch which is open when no external forces are applied, it will be understood by those skilled in the art that it may readily be converted to a so-called normally-closed switch. Such conversion may be effected by reversal of the polar relation of magnets 22 and 23. In particular magnet 22 may be positioned oppositely in bore 24 so that pole N of magnet 22 is arranged to engage electrode I 9, or magnet 23 may be rotated half of a revolution with respect to shaft 4. In either case, under normal conditions, when no force is applied to button 55, unlike magnetic poles of magnets 22 and 23 are in proximity and switch I is closed. Depression of button l5 causes like poles to be brought into proximity, thereby opening switch I as previously described. Fig. 5 shows an arrangement wherein magnet 22 is positioned in bore 24 in an opposite relation to the position shown in Fig. 1,

It will be noted that a primary feature of my invention is the use of forces of magnetic attraction and repulsion, rather than mechanical forces or the like, between the actuating and bridging elements of a switching mechanism, such magnetic forces being readily transmittable through substantial thicknesses of non-magnetic materials. Accordingly, it is possible to enclose the electrodes and bridging element of a switching mechanism completely within an electrostatic shielding device, and to cause forces required to actuate the switch to act through such a shield. Such an arrangement is exemplified in the embodiment herein described by the relationship of electrodes l9 and 2D, and bridging element 22, electrode I9 being arranged to shield electrostatically electrode 20 and bridging element 22 contained therewithin.

It will be further noted that the forces of magnetic attraction and repulsion utilized to actuate bridging element 22 tend to cause a $0- called magnetic snap action thereof, comparable to mechanical snap actions in conventional toggle mechanisms. Such a snap-action, provides a time delay between motion of actuator I0 and bridging element 22, which has been found to be particularly advantageous in the embodiment of my invention herein described. In effect, switch mechanism I, as represented in Fig. 1, is not closed until actuator I0 is depressed through substantially its full inward travel. Likewise, if switch mechanism 1 is thus closed, opening thereof is not effected until actuator I0 is released through substantially its full return travel. The resultant effect of such delayed action is to assure maintenance of switch mechanism l in a closed condition for a finite time following actuation thereof from an open condition, by manipulation of actuator 10.

Another feature of my invention resides in the limitation of mechanical forces which may be developed within switching mechanism l by actuation thereof. Since the extremities of travel of magnet 22 are fixed relative to magnet 23, the forces developed by magnetic interaction thereof are limited by well-known magnetic force-distance relationships, Such limitation of forces permits elimination or control of extraneous piezo-electric voltage effects which might be de- Veloped in insulator 2| by forces applied thereto,

Although my invention has been described as applied to an electrometer apparatus, it will be obvious to those skilled in the art that it may well be used in a variety of other applications. For example, in an application requiring a switch to be actuated through a wall of a sealed pressure or vacuum vessel, my invention would be readily adaptable. As has been pointed out, the absence of mechaniscal linkages and the like, and the use in place thereof of magnetic forces, between an actuating element and a bridging element in a switching mechanism is a particular feature of the invention. And while in the embodiment of my invention herein disclosed, I have chosen to show magnets of the permanent type, it will be obvious that such magnets may readily be replaced by magnets of the electric type, having windings excited from sources of electrical potential, which would oiTer additional possibilities for variation in the application of my invention, such as, for example, electrical remote control of a switching operation.

While a preferred embodiment of my invention has been described, it will be understood that my invention may well take other forms and it is intended therefore to cover in the appended claim all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

A magnetically actuated electrical switching device of the type described, comprising nonmagnetic inner and outer coaxial electrodes spaced apart and electrically insulated each from the other, said inner electrode having an inwardly extending radial bore, an electrically conductive permanent bar magnet slidably positioned within said bore so that the bar magnet can close an electrical circuit between said electrodes or open such circuit selectively depending upon its position, an actuating magnet having north and south magnetic poles positioned outside and adjacent to said outer electrode, and means to place the north and south magnetic poles of said actuating magnet selectively in proximity to the outer end of said bar magnet, whereby the bar magnet is moved selectively to its closed-circuit position or its open-circuit position by magnetic attraction and magnetic repulsion respectively.

JOHN E. BIGELOW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 565,985 Hoffman Aug. 18, 1896 2,012,153 Bates Aug. 20, 1935 2,319,010 McLeod May 11, 1943 2,323,910 Hubbell July 13, 1943 2,339,087 Mantz Jan, 11, 1944 2,353,740 Malone July 18, 1944 2,410,746 Raettig Nov. 5, 1946 

